This is the first application filed for the present invention.
Not Applicable.
The present invention relates to mapping communications paths through a communications network, and in particular to label selection for end-to-end label switched traffic through a communications network.
Optical communications networks have recently become established, as the preferred backbone for data communications because of the high bandwidth capacity of the optical fiber links. In the modern network space, packetized data traffic of multiple different protocols (e.g. internet protocol, frame relay, asynchronous transfer mode, etc.) is transported over a common network infrastructure. Each protocol provides its own packet (or frame) size and format standards. Additionally, some protocols (e.g. IP) are specifically designed to allow packets having widely varying lengths. New routing protocols, for example the multi-protocol label switching (MPLS) protocol have been proposed to facilitate multi-protocol traffic across a common network infrastructure.
Under the MPLS protocol, label switched packets (LSPs) are propagated across the network hop-by-hop along a path that is set up at the beginning of a communications session. In general, the label assigned to the LSP can be different for each hop, with the label conversion being performed by the node serving the respective hop. Where the network is designed for wave division multiplex (WDM) transport of data traffic, it is desirable to use a data channel (or wavelength) as the label assign to an LSP through a respective hop. In this case, end-to-end transport of an LSP through an MPLS path requires a change of wavelength in the node serving each hop.
However, the, modern network space is composed of a mixture of agile cross-connects (i.e. cross-connects capable of wavelength conversion from input to output) and non agile cross-connects (i.e. cross-connects that are unable to do wavelength conversion). Because MPLS normally requires that the labels (i.e. the wavelengths) must be changeable at every hop, non agile cross-connects within the network cannot participate in an MPLS end-to-end optical path. This restriction forces MPLS traffic to be routed around non-agile cross-connects, and serves as a barrier to the widespread implementation of MPLS.
A technique which allows non-ageile cross-connects to participate in MPLS end-to-end optical paths is therefore highly desirable.
An object of the present invention is to provide a technique which enables an MPLS end-to-end optical path to be mapped through a communications network, in which at least one and possibly all of the nodes participating in the path are non-agile.
A further object of the present invention is to provide a technique enabling an MPLS end-to-end optical path to be mapped across a communications network using a common label (e.g. wavelength) for every hop of the path, so that inter-hop label conversion is not necessary.
Accordingly, an aspect of the present invention provides a method of label selection for end-to-end transport of label switched traffic through a communications network between a source node and a destination node. A request message is launched toward the destination node from the source node. The request message includes a label list having one or more label identifiers indicative of respective corresponding labels available for use by the source node. The label list is revised, at a cross-connect service each successive hop between the source node and the destination node, based on labels available for use by each respective hop, to produce a reduced label list. The reduced label list includes label identifiers indicative of respective corresponding labels available for end-to-end transport of label switched traffic between the source node and the destination node.
A further aspect of the present invention provides communications network adapted for end-to-end transport of label switched traffic through the communications network.
The communications network comprises a source node, a destination node, and at least one cross-connect intermediate the source node and the destination node. The source node is adapted to launch a request message toward a destination node. The request message includes a label list having one or more label identifiers indicative of respective corresponding labels available for use by the source node. Each cross-connect is adapted to revise the label list based on labels available for use over a successive hop served by the cross-connect, to produce a reduced label list.
A still further aspect of the invention provides a cross-connect of a communications network adapted for end-to-end transport of label switched traffic through the communications network between a source node and a destination node. The cross-connect includes a label availability table, a buffer and a processor. The label availability table includes label identifiers indicative of labels available for a successive hop served by the cross-connect. The buffer is adapted to receive a request message propagated through the communications network from the source node. The request message includes a label list having label identifiers indicative of labels available for conveying label switched traffic between the source node and the cross-connect. The processor is adapted to revise the label list included in the received request message, based on the label availability table, to produce a reduced label list.
The communications network may be adapted for wave division multiplex (WDM) transport of label switched traffic, each label comprising a respective data transport wavelength.
The label switched traffic may include multi-protocol label switched (MPLS) traffic.
In an embodiment of the invention, the step of revising the label list comprises, at each cross-connect serving a successive, hop toward the destination node, a step of intersecting the label list with a set of label identifiers indicative of labels available for use over the hop. A request rejection message may be sent to the source node if the reduced label list is empty.
If the reduced label list included with the request message received by the destination node contains at least one label identifier, then one of the label identifiers is selected from the reduced label list. An end-to-end label switched path is then set up between the source node and the destination node using the respective label corresponding to the selected label identifier. The label identifier may be selected at random from the reduced label list.
The step of setting up an end-to-end label switched path may include sending a mapping message containing the selected label identifier from the destination node toward the source node, the mapping message retracing the path traversed by the request message. Upon receipt of the mapping message at the cross-connect serving each hop, the corresponding label indicated by the, selected label identifier is assigned to the end-to-end label switched path, if the label is still available for use by the hop.
A mapping failure message may be sent to the destination node if the label corresponding to the selected label identifier is not available for use by the hop. In this case, upon receipt of the mapping failure message by the destination node, the reduced label list may be stripped by removing the selected label identifier. If the thereby stripped label list is empty, a request rejection message may then be sent to the source node. Otherwise, if the stripped label list contains at least one label identifier, a new label identifier may be selected from the stripped label list, and an end-to-end label switched path set up between the source node and the destination node using the respective label corresponding to the newly selected label identifier.